VulnerabilityPublished 9 Feb 2026

CVE-2026-25905: mcp-run-python · Improper Isolation or Compartmentalization

Affects mcp-run-pythonSource CVE Database V5

Not known to be exploited · CVSS 5.8 Medium.

Data as of 26 Oct 2026, 09:08 UTC

CVSS 3.1 base score

5.8Medium

How severe the flaw is on the 0–10 CVSS scale.

EPSS: 0.2% chance of exploitation in 30 days – higher than 10% of CVEsExploit Prediction Scoring System: the likelihood attackers will use this flaw soon.

CVSS:3.1/AV:N/AC:H/PR:N/UI:R/S:C/C:L/I:L/A:L

Attack Vector: Network
Attack Complexity: High
Privileges Required: None
User Interaction: Required
Scope: Changed
Confidentiality: Low
Integrity: Low
Availability: Low

Bold values are the worst case: easiest to exploit or largest impact.

Attack Vector: Network: The vulnerable component is bound to the network stack and the set of possible attackers extends beyond the other options listed, up to and including the entire Internet. Such a vulnerability is often termed 'remotely exploitable' and can be thought of as an attack being exploitable at the protocol level one or more network hops away (e.g., across one or more routers).
Attack Complexity: High: A successful attack depends on conditions beyond the attacker's control. That is, a successful attack cannot be accomplished at will, but requires the attacker to invest in some measurable amount of effort in preparation or execution against the vulnerable component before a successful attack can be expected. For example, a successful attack may require an attacker to: gather knowledge about the environment in which the vulnerable target/component exists; prepare the target environment to improve exploit reliability; or inject themselves into the logical network path between the target and the resource requested by the victim in order to read and/or modify network communications (e.g., a man in the middle attack).
Privileges Required: None: The attacker is unauthorized prior to attack, and therefore does not require any access to settings or files to carry out an attack.
User Interaction: Required: Successful exploitation of this vulnerability requires a user to take some action before the vulnerability can be exploited.
Scope: Changed: An exploited vulnerability can affect resources beyond the security scope managed by the security authority of the vulnerable component. In this case, the vulnerable component and the impacted component are different and managed by different security authorities.
Confidentiality: Low: There is some loss of confidentiality. Access to some restricted information is obtained, but the attacker does not have control over what information is obtained, or the amount or kind of loss is limited. The information disclosure does not cause a direct, serious loss to the impacted component.
Integrity: Low: Modification of data is possible, but the attacker does not have control over the consequence of a modification, or the amount of modification is limited. The data modification does not have a direct, serious impact on the impacted component.
Availability: Low: Performance is reduced or there are interruptions in resource availability. Even if repeated exploitation of the vulnerability is possible, the attacker does not have the ability to completely deny service to legitimate users. The resources in the impacted component are either partially available all of the time, or fully available only some of the time, but overall there is no direct, serious consequence to the impacted component.

Definitions: FIRST CVSS v3.1 specification.

Exploitation evidence

Disclosed: evidence found.
CVE published 9 Feb 2026
Detectable: no evidence on record.
No public nuclei template indexed
Weaponised: no evidence on record.
No public exploit code indexed in Metasploit or Exploit-DB
Exploited in the wildExploited: no evidence on record.
Not in CISA KEV and no source reports exploitation
Observed by OffSeq MirageSeen by Mirage: no evidence on record.
No attack traffic recorded by OffSeq Mirage sensors

A missing step is not evidence of safety. Sources: cve.org (opens in a new tab), the Metasploit, Exploit-DB and nuclei-templates index as of 26 Oct 2026.

Disclosed: The CVE record is public on cve.org. Its publication is t = 0.
Detectable: A public nuclei template can find exposed instances, for defenders and attackers alike.
Weaponised: Public exploit code exists in Metasploit or Exploit-DB, or CISA SSVC reports a public proof of concept.
Exploited in the wild: CISA KEV lists it, CISA SSVC rates exploitation active, or a source reports attacks.
Observed by OffSeq Mirage: OffSeq Mirage honeypot sensors recorded attack traffic for this CVE, or found exposed hosts without attack traffic.

Moments are spaced evenly, not to scale; a dashed line marks a gap of six months or more. Deltas count from t = 0. Sources that give only a date (CISA KEV, Exploit-DB, or a time of exactly 00:00Z) read “same day” rather than hours. Metasploit modules carry the flaw’s disclosure date, not their release date, and nuclei templates carry no date, so both appear above but not on the timeline.

What to do

Affected software

Product	Affected	Fixed in
PyPImcp-run-python`pkg:pypi/mcp-run-python`Other threats	Affected =0	Fixed in–

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AI-suggested

Given that 'mcp-run-python' is archived and unlikely to receive patches, European organizations should prioritize migrating away from this project to actively maintained alternatives that enforce strict isolation between Python and JavaScript environments. Where migration is not immediately feasible, organizations should implement strict sandboxing to isolate Python execution contexts, preventing Python code from accessing or modifying the JS environment or underlying system resources. Employing WebAssembly security best practices, such as limiting Pyodide API exposure and using content security policies (CSP) to restrict script execution, can reduce attack surface. Additionally, organizations should implement robust input validation and user interaction controls to prevent injection of malicious Python code. Monitoring and logging Python and JS interactions can help detect anomalous behavior indicative of exploitation attempts. Regular security assessments and code reviews focusing on integration points between Python and JavaScript are recommended. Finally, educating developers and users about the risks of executing untrusted Python code in these environments is essential to reduce user interaction-based exploitation.

Description

CVE-2026-25905 is a medium severity vulnerability affecting the 'mcp-run-python' project, where Python code executed via 'runPython' or 'runPythonAsync' is not properly isolated from JavaScript code. This improper compartmentalization (CWE-653) allows Python code to manipulate the JavaScript environment through Pyodide APIs, potentially enabling an attacker to hijack the MCP server and perform malicious activities such as tool shadowing. The vulnerability has a CVSS score of 5.8, indicating moderate risk, with network attack vector, high attack complexity, no privileges required, and user interaction needed. The project is archived and unlikely to receive patches, increasing the risk for users still relying on it. There are no known exploits in the wild as of now. European organizations using this tool or similar environments integrating Python and JavaScript without proper isolation are at risk, especially those in critical infrastructure or software development sectors. Mitigation requires isolating Python execution environments, restricting Pyodide API access, or migrating away from the unmaintained project. Countries with strong software development ecosystems and critical infrastructure relying on such tools, including Germany, France, the UK, and the Netherlands, are more likely to be affected.

Impact

For European organizations, the impact of CVE-2026-25905 can be significant in contexts where the 'mcp-run-python' project or similar Python-JavaScript integration tools are used. Successful exploitation could lead to unauthorized control over MCP servers, enabling attackers to manipulate server operations, exfiltrate sensitive data, or disrupt services. This could affect software development environments, cloud services, or web applications relying on embedded Python execution. The compromised integrity and availability of affected systems could disrupt business operations, especially in sectors like finance, healthcare, and critical infrastructure that rely heavily on secure and stable IT environments. Additionally, the ability to perform tool shadowing could allow attackers to persist undetected, complicating incident response and increasing the risk of data breaches or sabotage. Since the project is archived and unpatched, organizations continuing to use it face prolonged exposure. The medium CVSS score reflects moderate risk, but the changed scope and potential for server hijacking elevate the threat in high-value environments.

Summary

CVE-2026-25905 identifies a vulnerability in the 'mcp-run-python' project, specifically in the way Python code executed via 'runPython' or 'runPythonAsync' functions interacts with the JavaScript (JS) environment. The core issue is improper isolation or compartmentalization (CWE-653), where Python code is not sandboxed and can leverage Pyodide APIs to modify the JS environment. Pyodide is a WebAssembly-based Python runtime that allows Python code to run in browsers or JS environments. Because the Python code can manipulate the JS environment, an attacker who can inject or execute Python code can hijack the MCP server, potentially leading to unauthorized control or manipulation of server-side processes. This can facilitate malicious activities such as MCP tool shadowing, where attackers stealthily replace or interfere with legitimate tools. The vulnerability has a CVSS 3.1 base score of 5.8, reflecting a medium severity level. The attack vector is network-based (AV:N), but the attack complexity is high (AC:H), meaning exploitation requires specific conditions or knowledge. No privileges are required (PR:N), but user interaction is necessary (UI:R), such as tricking a user into executing malicious Python code. The scope is changed (S:C), indicating that exploitation affects components beyond the vulnerable component itself. The project is archived and unlikely to receive fixes, leaving users exposed unless they implement their own mitigations or migrate. No known exploits have been reported in the wild, but the risk remains due to the lack of maintenance. This vulnerability is particularly relevant for environments that integrate Python and JavaScript, especially where Pyodide is used without strict sandboxing or isolation controls.

CWE-653Improper Isolation or Compartmentalization (opens in a new tab)
Class weaknessOWASP Top 10 A06:2025: Insecure Design (opens in a new tab)
The product does not properly compartmentalize or isolate functionality, processes, or resources that require different privilege levels, rights, or permissions.
Architecture and Design
Break up privileges between different modules, objects, or entities. Minimize the interfaces between modules and require strong access control between them.
OWASP Cheat Sheets
Secure Design Principles (opens in a new tab)
From MITRE CWE, MITRE CAPEC and OWASP (Top 10, OpenCRE).

References

research.jfrog.com/vulnerabilities/mcp-run-python-lack-of-isolation-mcp-takeover-jfsa-2026-001653030/ (opens in a new tab)

Community reviews

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Exploitation evidence

What to do

Affected software

Description

AI analysisMachine-generated, updated 16 Feb 2026, 13:36 UTC

WeaknessesCWE-653

Technical details

References

Community reviews

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